The present invention relates to a pressure-responsive reed valve especially adapted for use in a system for introducing the secondary air by utilizing the negative pressure produced in an exhaust system, especially at a portion in the vicinity of an exhaust port of an internal combustion engine.
In general, a conventional reed valve comprises a base formed with at least one aperture through which flows a fluid, a rubber seat embedded in the base so as to surround the aperture at the inner peripheral surface thereof, and a reed made from sheet steel and having its one end securely fixed to the base so that it is forced to seat on the seat, thereby closing the aperture and to move away from the seat at its free end thereby opening the aperture. The inner peripheral surface of the seat is in line with the inner peripheral wall of the aperture, and the upper edge of the inner peripheral surface of the seat which engages with the free end portion of the reed is slightly beveled or rounded.
When the reed valve of the type described above is installed in the secondary air supply system of the type described above, the reed is forced to move away from the seat when the pressure of exhaust gases drops negative, whereby the aperture is opened to draw the secondary air. When the pressure of exhaust gases rises positive the reed is forced to strike against the seat, thereby closing the aperture, whereby the suction of the secondary air into the exhaust system may be interrupted.
In accordance with the type of an engine and the construction and arrangement of its exhaust system and secondary air intake system, however, the pressure of exhaust gases rises extremely high in a special speed range under a heavy load, especially in a speed range in which the exhaust gases flow reversely through the reed valve toward the secondary air intake system. As a result the reed is forced to violently strike against the seat under increased force and consequently it forcibly depresses the seat. The resultant deformation of the seat is especially remarkable at the portion which engages with the free end portion of the reed. Moreover, the on-off operations of the reed valve are as high as several tens to one hundred and several tens times per second so that this portion of the seat is subjected to extreme stress concentration and fatigue. As a consequence, the rubber seat is subjected to cracking and fracturing within a short time.